Sphingomyelin fatty acid structure

Figure 1. The structures of two phospholipids. Structure A represents a classic glycerophospholipid, POPC, and it is composed of choline, phosphate, glycerol, and two fatty acids. Structure B is an example of a sphingomyelin, and if is composed of choline, phosphate, sphingosine, and only one fatty acid.

Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units (a) phos-phatidylethanolamine (b) sphingomyelin (c) galactosyl-cerebroside (d) ganglioside (e) cholesterol. 

Structural components and function of sphingomyelin The alcohol sphingosine attached to a long-chain fatty acid produces a ceramide. Addition of a phosphorylcholine produces the phospholipid sphingomyelin, which is the only significant sphingophospholipid in humans. It is an important constituent of myelin. 

Fig. 2. Structures of (a) the sphingolipids sphingomyelin and galactocerebroside (b) cholesterol. R1 represents the hydrocarbon chain of fatty acids.

Deducing Lipid Structure from Composition Compositional analysis of a certain lipid shows that it has exactly one mole of fatty acid per mole of inorganic phosphate. Could this be a glyc-erophospholipid A ganglioside A sphingomyelin ... 

The major fatty acids of GD3 and GM3 (the major gangliosides of bovine milk) are 22 0, 23 0, 24 0 and 16 0, with both species of ganglioside having similar fatty acid compositions (Table 1.14). These fatty acids are also a feature of the sphingomyelin structure. Martin et al. (2001), who... 

Biochemistry and molecular biology of structural components. The schistosome tegument contains several phospholipids, the most abundant being phosphatidylcholine (57%), phosphatidylethanolamine (17%), sphingomyelin, lysophosphatidylcholine, phosphatidylinositol and cerebroside glycolipids (7,34). Palmitic acid and oleic acid are the most abundant fatty acids (35). These molecules are derived from the host, as schistosomes are unable to synthesize cholesterol or long-chain fatty acids de novo (36). However, schistosomes can interconvert fatty acids and cleave the polar head from some phospholipids (37). 

Fig. 33.5. General structures of the sphin-golipids. The backbone is sphingosine rather than glycerol. Ceramide is sphingosine with a fatty acid joined to its amino group by an amide linkage. Sphingomyelin contains phos-phocholine, whereas glycolipids contain carbohydrate groups.

Cell membranes have a fluid mosaic structure. The term fluid conveys the fluid (flexible) or liquid-like nature of the cell membrane. The term mosaic conveys the complex nature of cell membranes in terms of their structure and composition. Not only does the lipid bilayer contain different lipids (phosphoglycerides, plasmalogens, sphingomyelins, glycolipids, cholesterol), it also contains a variety of proteins essential to cell function. The physiological function of a membrane depends on its fluidity, which varies with the relative amounts of saturated fatty acids, unsaturated fatty acids, and cholesterol. 

Lipids occur widely in nature. For examples, phospholipids are the main building blocks of biological membranes. Lipids exist in a variety of distinct forms, such as fatty acids, acylglycerols, phospholipids, sphingomyelins, glycosphingolipids, gangliosides, steroids, bile acids, prostaglandins, and leukotrienes. Some of lipids are structurally simple molecules, but others are complex molecules. Many are amphiphilic compounds. 

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